Great one!
How my dad remembered it, there was occasionally a sound of aircraft engines that was very strange and it took a long time to search the air for sight of the airplane. When they would sight the airplane it would be a tiny, silver or white-looking cross way up in the atmosphere. His assumption was that it was one of the Ju-86s and he definitely said that his guys were told the airplane had Diesel engines, thus the odd sound. As I remember it this was when he was stationed in Tunisia, at least it was during his time in North Africa.